What shall we infer from all these theories? That the obliquely-oval pelvis of Naegele is not a single type, but presents several clearly-marked varieties, which may be reduced to three, viz.: 1. The most frequent form is distinguished by the fusion of the sacrum with the ilia, with conse quent atrophy of the bones composing the articulation. (NaegelCs pel vis.) 2. The second variety is characterized by atrophy of the ilium and one-half of the sacrum, but without anchylosis. 3. In the third there is simply oblique contraction, without the other conditions.
The Transversely-contracted Pelvis.
This pelvis is characterized by anchylosis of both sacro-iliac articula tions, with absence, or rudimentary development, of the ake of the sa crum. The sacral vertebrae are straight and the sacrum presents a convex ity transversely, instead of its usual concavity. The sacrum is deeply depressed in the pelvis, so that the posterior extremities of the iliac bones project prominently, and the posterior superior spines are closely approxi mated. There is little, if any, curve to the os innominatum. The iliac bones are flattened anteriorly and unite at a very acute angle at the sym physis. As a result, there is marked lateral contraction, so that the pelvis appears to be composed of the two halves of two obliquely-oval pelves. The principal alteration in these pelves consists in the transverse narrow ing, which increases from the superior to the inferior strait, so that the latter is in some cases represented only by a long narrow cleft. This variety of pelvis is not very common, only thirteen having been described.
According to Schroeder, anchylosis is not the original lesion, but is duced in consequence of the pressure of the trunk; as the sacrum is forced downward under the weight of the trunk friction occurs, which culmi rtates in adhesive inflammation of the sacroiliac synchondroses, with re sulting anchylosis. The pelvis preserves the infantile form, except that the sacrum sinks more deeply into the pelvis, and the ilia, on account of the pressure exerted through the femora, are more approximated, so that the transverse diameters are much shorter in proportion than in the new born. The sinking of the promontory shortens the conjugate diameter of the brim, but as there is no transverse widening of the pelvis, the symphysis not only does not approach the promontory, but even appears to be thrust forward; the conjugate is thus again increased, so that it generally varies very little from the normal length.
Figs. 46-49 represent a very rare form, described by Naegel6 and Grenser. The woman died after the Cesarean section.
Pelves altered by Deviation of the Vertebral Column.—(Lordosis, scoliosis, kyphosis, kypho-scoliosis, kypho-sciolio-rachitic, spondylizema, and spondylolisthesis.) It is only of late years that the influence of deviations of the spine has really been studied. Cazeaux says: " We must not think that non-rachitic spinal curvature has no influence on the direction and form of the pelvis; but, as a rule, it is only in old subjects that spinal curvatures, that have developed after infancy, produce changes in the shape and direction of the pelvis, so that these possess but slight interest for the obstetrician." Although rnchitic curvatures of the spine are not the principal cause of pelvic deformity, they exaggerate the narrowing and irregular shape of the pelvis. The main alteration consists in a curve from before backward, most marked at the lumbo-sacral junction, in consequence of which the Vox,. 111-4 pelvis resembles Naegele's. Choisil, studying pelves with regard to the shortening of the transverse diameter of the outlet, divides them into the following varieties: 1. Pelves deformed by straightness of the vertebral column, by scoliosis, or kyphosis. 2. Obliquely-oval pelves, those de formed by double anchylosis, simple luxation, amputation, arrest of de velopment, and by osteomalacia. He believes, with Pinard, that every curvature of the spine in the young, whether due to scoliosis, or to ky phosis, causes retrocession of the base of the sacrum, leading to lengthen ing of the conjugate diameter of the brim, and proportional shortening of the transverse diameter of the outlet.
a. The Influence of Lordosis on the Shape of the Pelvis.—Increased in clination of the pelvis is the initial change; the anterior part of the pelvis tilts downwards, while the posterior is thrown upwards, this being due to the fact that the patient, when standing, bends forward in order to bring the centre of gravity over a lino joining the heads of the femora. When lordosis and rickets are associated the promontory projects more, causing shortening of the antero•posterior diameter.